Non-contact gear devices include magnetic gear devices. A magnetic gear device includes a first movable element and a second movable element in which a plurality of magnetic pole pairs having different magnetic poles are placed on an operating surface side at equal intervals. For example, the first movable element and the second movable element have a cylindrical shape, a disk shape or a flat plate shape. A plurality of magnetic materials functioning as pole pieces are placed between the first movable element and the second movable element at equal intervals. When the first movable element is moved, the second movable element is moved by magnetic interactions between the magnetic pole pairs each included in the first movable element and the second movable element. A gear ratio of the second movable element with respect to the first movable element is decided depending on a combination of the numbers of magnetic pole pairs of the first movable element and the second movable element. The operating surface mentioned here refers to facing surface sides of the first movable element and the second movable element that face each other with the plurality of magnetic materials interposed therebetween.
There are magnetic gear devices such as a cylindrical rotary type magnetic gear device including an internal rotor and an external rotor as the first movable element and the second movable element or a cylindrical linear type magnetic gear device including an internal column and an external column as the first movable element and the second movable element (for example, see Non-Patent Document 1 and Non-Patent Document 3). The cylindrical rotary type magnetic gear device includes a cylindrical internal rotor, a cylindrical external rotor into which the internal rotor is fitted at an interval, and a cylindrical intermediate yoke inserted between the internal rotor and the external rotor at an interval. On each of an outer peripheral surface of the internal rotor and an inner peripheral surface of the external rotor, a plurality of magnetic pole pairs constituted by an N pole magnet and an S pole magnet are placed in a circumferential direction. The intermediate yoke holds a plurality of ferromagnetic magnetic materials in the circumferential direction at equal intervals.
When the external rotor rotates, the internal rotor rotates by the magnetic interaction between the magnetic pole pairs each included in the internal rotor and the external rotor. Herein, when the numbers of the magnetic poles each placed in the internal rotor and the external rotor are set to Ph and Pl, an alternating magnetic field is generated in a radial direction along with the rotation of the internal rotor and the external rotor. Herein, when the number of magnetic materials held by the intermediate yoke is set to Ns, the alternating magnetic field mainly includes a Phth harmonic component, an (Ns−Ph)th harmonic component and an (Ns+Ph)th harmonic component (for example, see Non-Patent Document 2).
Because the internal rotor and the external rotor rotate in synchrony with the alternating magnetic field including the three harmonic components, the number Pl of the magnetic pole pairs placed in the external rotor is set to (Ns−Ph) or (Ns+Ph) (for example, see Non-Patent Document 2). In other words, the number Ns of the magnetic materials held by the intermediate yoke is set to (Ph+Pl) or (Pl−Ph).
FIG. 10 is a schematic assembly view that shows an example of a cylindrical rotary type magnetic gear device of the related art. The magnetic gear device includes an internal rotor 100, an intermediate yoke 200, and an external rotor 300. On an outer peripheral surface of the internal rotor 100, three magnetic pole pairs 102 including a magnet 102a with N pole at outer side and a magnet 102b with S pole at outer side magnetized in a thickness direction are placed in the circumferential direction. Furthermore, on an inner peripheral surface of the external rotor 300, seven magnetic pole pairs 302 including a magnet 302a with N pole at inner side and a magnet 302b with S pole at inner side magnetized in a thickness direction are placed in the circumferential direction. Thereby, the magnetic gear device shown in FIG. 10 has a gear ratio of 3/7.
The intermediate yoke 200 holds a total of ten magnetic materials 202 of the numbers 3 and 7 of the magnetic pole pairs 102 and 302 included in each of the internal rotor 100 and the external rotor 300 in the circumferential direction at equal intervals. For example, the intermediate yoke 200 is manufactured by fixing each magnetic material 202 to a resin formed in a cylindrical shape (see Patent Document 1). The alternating magnetic field including a third harmonic component, a seventh harmonic component and a thirteenth harmonic component generated by the magnetic pole pairs 102 and 302 intersects with the intermediate yoke 200 in a radial direction.
Patent Document 1: Pamphlet of International Patent Publication WO 2009/087408
Non-Patent Document 1: K. Atallah, “Design, analysis and realization of a high-performance magnetic gear,” IEE Proceedings-Electric Power Applications, U.K., March, 2004, volume 151, No. 2, pages 135 to 143
Non-Patent Document 2: Tetsuya Ikeda, Kenji Nakamura and Osamu Ichinokura “A Way to improve Efficiency of Permanent-Magnet Magnetic Gears” Journal of Magnetic Society, 2009, volume 33, No. 2, pages 130 to 134
Non-Patent Document 3: K. Atallah, J. Wang, D. Howe, “A high-performance linear magnetic gear,” Journal of Applied physics, U.S., 2005, volume 97, No. 10, 10N516—pages 01 to 03